Eukaryon, vol. 9, March 2013, Lake Forest College Grant Proposal
The use of algal chloroplasts to express Plasmodium falciparum Circumsporozoite Protein and Pfs25 surface antigens in a vaccine aimed to induce protective antibody responses in mice and mosquitoes
Christian Athens* be effectively expressed and thus increase antibody Department of Biology responses in hope of preventing infection of blood cells in Lake Forest College, mice. Lake Forest, Illinois 60045 Specific Aims
Introduction 1. Use C. reinhardtii chloroplasts as a recombinant system to effectively produce specific P. falciparum surface Malaria is a major issue in tropical and subtropical regions of protein antigens and elicit increased antibody the world. There are nearly 200 million new cases of malaria production in mice and mosquitos. We will assess the and 1 million deaths per year (Wiki, 2012). P. falciparum immunogenicity of the recombinant Pfs25 and CSP causes the most deadly form of the disease and is surface proteins by measuring the amount of antibodies transmitted by the female Anopheles mosquito (Wiki, 2012). produced in vaccinated mice. Our hypothesis predicts The circumsporozoite protein (CSP) is a prominent surface that there will be significant level of antibodies produced antigen of the P. falciparum parasite during its erythrocytic against the specific antigen. stage. The CSP has been a prime target for vaccine 2. To determine whether the heightened antibody development to fight blood stage infection; among the most production will inhibit the various stages of the parasite, promising is the RTS,S viral vector vaccine by we will test to see if vaccinated mice show resistance to GlaxoSmithKline, but has not been effective enough to be sporozoite inoculation and if mosquitos fed antisera licensed (Ballou, 2009). The uses of bacterial and viral from vaccinated mice will experience hindered vectors have been common among attempts to develop an transmission. This will be done by testing the blood of effective vaccine but remain expensive to produce and not the mice for sporozoite development and by dissecting always effective at expressing the target antigen, which may mosquitos to see if any ookinetes develop in the explain why none have been licensed (Danuvillee et al., mosquitos. 2010). Recent research suggests that algal chloroplasts may be utilized as effective recombinant system for Plasmodium Experimental Proposal surface antigens (Danuvillee et al., 2010). The algae are cheap and easy to produce in large quantities, genetically In the first experiment we will measure the immunogenicity tractable, and have been used to produce protein subunit of the chloroplast recombinant vaccine. The experiment will vaccines (Danuvillee et al., 2010). require a total of eighty mice, all of which will be assigned to A study published last spring by Gregory et al. (2012) one of four vaccine variants. The mice will either be given and colleagues used the algae Chalamydomonas reinhardtii the CSP + Pfs25, CSP without Pfs25, Pfs25 without CSP, or to express the P. falciparum surface protein 25 (Pfs25) in a the negative control that does not express either. vaccine and found that the vaccine elicited antibody Vaccinating two different groups with each antigen alone will responses in mice and blocked sexual development of the allow us to determine if immunogenicity is greater when the parasite in mosquitoes (Gergory et al., 2012). The Pfs25 is a two antigens are not combined in the recombinant surface protein expressed during the sexual stages of P. chloroplast system. Twenty mice will be assigned to each falciparum (Gergory et al., 2012). Previous research has group and we will wait two weeks before analyzing mice shown that C. reinhardtii can effectively express P. antisera. Antibody titers will be measured by ELISA against falciparum surface antigens and induce antibody response in affinity purified CSP and Pfs25 (Gergory et al., 2012). This mice and mosquitos (Gergory et al., 2012). Furthermore, will allow us to quantify the relative amount of antibodies over the years, the CSP antigen’s immunogenicity has been produced in response to the various vaccine assignments shown to elicit strong antibody responses in numerous (Gergory et al., 2012). studies; however using C. reinhardtii to express CSP and The second part of the experiment will depend on the Pfs25 antigens together has not been studied and serves as results measured by ELISA. If our hypothesis is correct that a potential vaccine candidate (Okitsu et al., 2007) (Wang et the CSP + Pfs25 vaccine will induce heightened antibody al. 1995). response, then the antisera from the CSP + Pfs25 Given this, I would like to develop a vaccine against P. vaccinated mice will then be fed to female Anopheles falciparum using the C. reinhardtii chloroplasts to express mosquitoes along with P. falciparum gametocytes to recombinant CSP and Pfs25 surface antigens. determine if the antibodies to the CSP+Pfs25 antigens will Hypothesis block transmission. The female Anopheles mosquitoes will I hypothesize that using C. reinhardtii chloroplasts as a then be dissected after two weeks to analyze oocyte recombinant system to express the CSP and Pfs25 surface production (Gergory et al., 2012). The control mosquitoes antigens will elicit increased antibody responses in mice and will be fed only the P. falciparum gametocytes. mosquitos, preventing P. falciparum infection and If the CSP+Pfs25 vaccine does in fact elicit increased transmission. The Pfs25 antigen has been shown to elicit antibody responses, we will also test if the extent of heightened antibody responses in mice and mosquitos but immunogenicity elicited by CSP+Pfs25 vaccine is enough to CSP has not been used in a chloroplast system (Gergory et provide resistance to sporozoites. The immunized and al., 2012). Given that the chloroplasts can be readily control mice will be administered 5000 live sporozoites to manipulated genetically, we predict that the CSP antigen will ensure that enough sporozoites are present for infection to ______occur. A hemocytometer will be used to analyze the blood cells and determine whether infection has been hindered. *The author wrote the grant proposal for Biology 320: Microbiology. Potential Outcomes Eukaryon, vol. 9, March 2013, Lake Forest College Grant Proposal
Given that previous studies, such as those done by Okitsu et al. (2007) and Wang et al. (1995), have shown increased antibody production with CSP and with Pfs25 vaccination, we predict that if the chloroplast can effectively express both recombinant antigens, we should expect to see increased antibody responses in mice vaccinated with CSP+Pfs25; furthermore, we expect to see little to no antibody production in the control mice. However, the genetic manipulation of recombinant CSP into chloroplasts has not been previously attempted; therefore, we cannot guarantee that CSP can be expressed by the algal chloroplasts. In the previously mentioned study done by Gregory et al. (2012), the Pfs25 chloroplast vaccine was effective in inducing antibody responses in mice and blocked transmission to mosquitoes. We expect our results to follow this same trend, unless the presence of CSP in the vaccine hinders expression of the Pfs25. If the CSP+Pfs25 vaccine does elicit increased antibody responses compared to the control, we would hope that this would provide resistance or at least some delay in blood cell infection.
Conclusion
This experiment would be the first to incorporate the CSP antigen in the C. reinhardtii Pfs25 recombinant chloroplast vaccine. It is important to experiment with the CSP antigen given its strong immunogenicity for antibodies that provide protection against infection of the blood cells. Incorporating CSP and Pfs25 into a single C. reinhardtii recombinant chloroplast vaccine that can effectively express both antigens and elicit antibody responses would provide protection to the individual being vaccinated, as well as block transmission in the mosquito. It is possible that this type of vaccine could be efficiently produced in mass quantities and at low cost, making it a very attractive candidate for vaccine design and development (Gergory et al., 2012).
References
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